The present invention relates generally to shift control device for a bicycle, and more particularly, to a twist-grip shift control device for shifting a bicycle transmission having a planetary gear mechanism for varying the relative angular position between an actuating member and a base member.
Generally, bicycle riders prefer a shift control device that is easy to function and requires little force to operate.
The conventional twist-grip type shift control device includes a cable winding member operatively engaged with a control grip rotatably mounted on the handlebar of the bicycle. In the conventional twist-grip shift control device, the ratio of rotational angle between the control grip and the winding member is 1:1. There have been attempts to decrease the operational force of the known twist-grip shift control devices by decreasing the diameter of the winding member. However, because the winding member of the known devices are installed coaxially with respect to the handlebar, it is not possible to have a winding member with a diameter that is smaller than the diameter of the handlebar.
The operational force may also be decreased by enlarging the diameter of the control grip. However, this type of engineering design is limited by the anatomical features of the human hand. An oversized control grip is ergonomically disfavored, especially for a bicycle rider having small hands. Additionally, the aesthetic appearance of a control grip is negatively impacted by an enlarged control grip. An increase in size of the control grip corresponds to an increase in weight of the shift control device, which is a disadvantage when it is desirable to minimize the weight of a bicycle and its components.
Accordingly, it is desirable to provide a shift control device that includes a gear mechanism for controlling the ratio of the rotational angle between the control grip and the winding member.
The present invention is directed to a twist-grip shifting device that avoids the large forces required to operate prior art twist-grip shifting devices.
A shift control device for a bicycle is disclosed having a planetary gear assembly for varying the relative angular position between an actuating member and a control member. In a preferred embodiment of the invention, the shift control device includes a control member engageable with a ring gear to drive a plurality of planetary gears about a fixed base member. The fixed base member preferably includes a sun gear integrally attached thereto. The planetary gears are preferably carried by an actuating member configured to pull and release a bicycle shift cable. Rotation of the planetary gears results in the tension or release of the bicycle shift cable. The shift control device can include a positioning mechanism for controlling the position of the actuating member relative the base member.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.